Waste heat boiler for aircraft



-Jan.27, 1942. ,N.`.PR|E 1 2,271,131' 'Y Y WASTE HEAT BOILER FOR AIRCRAT Filed May l, 1939 2 Sheets-Sheet l Ivg.

' 'mvEN-roR Jan. 27, 1942. Y N. c.` PRICE WASTE HEAT BOILER FOR AIRCRAFT 2 Sheets-Sheet 2 vFiled May 1, 1939 INVENTOR .Patented Jan. 27, 1942 raras PATENT WASTE HEAT BOILER FOR AIRCRAFT Nathan C. Price, Seattle, Wash., assigner to Sirius,

Corporation, a corporation of California Application May 1, 1939, serial No. 270,963

45 claims. (c1. 257-262) back pressure in the engine exhaust stack and ,the greatest waste heat absorption from the exhaust gases, with a minimum weight of structure. Another objective is -to provide a waste heat boiler which can withstand the severe vibra'.- tions, gas pulsations, and thermal stresses adja-` cent to an aircraft power plant installation. A still further objective is to provide amore eilicient type of heating surface, which can be readily fabricated by production methods. A ilnal objective of the invention is to provide a form of extended heat transfer surface with inherent thermal conductivity far greater than that of the heat resistant material forming the abrasion and corrosion resistant surface thereof, thereby'capable of withstanding the presence of high velocity gases.

The invention can also be used in industrial applications for liquid heaters or vapor generators but its most outstanding applicability is in waste heat utilization in airplanes.

The foregoing and other objects of the invention have been attained in the embodiment of the invention illustrated inthe drawings, in which:

Figure 1 is a representation oi' waste heat recovery structure of the new type viewed from the side. j y

Figure 2 is an end view oi the same waste heat recovery structure as in Figure 1. y

-Figure 3 is a diagrammatic representation of a section, along the axisof oneof the heat trans-* fer elements of Figure 1.

Figure 4 is va schematic representation of one side of the tube'wall and its extended surface,

along the axis of the boiler element of Figure 3. Figure 5 is a schematic diagram ofV one portion of a tube iin, along the axis oi' the boiler element.

Figures l and 2 represent the type of installation wherein my form of boiler is particularly yaluable. For example someboiler tube elements l are arranged in three superimposed pairs, bundled together in a'generally rectangular and elongated boiler casing 54. The axes A of the elements 1 are parallel to the greatest length o f the casing. Each element 1 is constructed iroin a relatively long tube 1 4 bearing numerous closely spaced ns 13 which are circular and transversely arranged with respect to the axes A.

The elements 'i have boiler fluid inlets 2 and v boiler iluid outlets 3 which join .in cross-over tubes 4 connecting the elements in series. A main liquid inlet 3l and a main vapor outlet 38' are provided. The elements 1 are swept by hot exhaust gas entering the bottom ofthe casing it from an engine exhaust stack 30. Ordinarily the. exhaust gas 'is ata temperature of about 1400 F. and the gas velocity is 300,1eet per second .or more.

The gas is turned at righi*l angles as it enters the space between the fins 13 and the sides 11 of the casing 54. After sweeping past the elements 'i the gas is expelled into a nozzle 49 diagonally opposite to the stack in respect tothe casing 5l. in the skin ,I6 of the aircraft. The nozzle ls'produces an exhaust gas jet, designated by the arrow X, substantially parallel tothe slip-stream, designated by the arrow Y. Accordingly the nozzle produces comparatively small`aerodynamic resistance and the jet results in a propulsive effect.

The sides I1 of the `casing 54 are deeply cor- -rugated to form circular envelopes for the edges f of the fins 13. This creates an eillclentpath for the flow between the tins because the sas is required to pass close to the periphery ofthe tube 14 eilectively sweeping the entire area of v the fins.

The use of exhaust gas for iet, propulsion requires a surplus pressure in the exhaust stack.

. Attendant with this gas pressure is an especially high resultant temperature inasmuch as the gas expansion cycle is not completed. Forthisreason my invention is of particular value in jet propulsion installations because of the high temperature durability offered. Indeed it has been found that conventional heat transfer surfaces will hardly endure in'such installations. more than a few hours due to the high temperature and high velocity abrasive action oi. the exhaust gases and carbon particles from the engine cylinder.

In Figure 3 the boiler element 'I is shown in greater detail. 'Ihe boiler iluid isadmitted from the inlet 2 into the interior of a co-axial spindle tube 93. The boiler fluid emerges from a bore 94 of the tube 93 as it impinges against an end plug 34. The fluid then reverses in'direction and passes around the outer surface oi' the tube.

A-helical land Il! on the external surface of the The nozzle extends through a cut-out 41 spindle causes high velocity helical flow of the boiler fluid.

This rotational eiect greatly increases the rate of heat transmission not only because of the high velocity produced but also because particles of liquid entrained in the boiler fluid are forced centrifugally against the bore of the tube 14. yThe rate vof rotation of the boiler` uid about the axis A may be approximately 100,000 revolutions per minute.

'Ifhe resulting rate of heat Vtransmission is of such magnitude that conventional extended heat, transfer surface cannot VVbe used without eventual failure due -to the tangential and radial Vthermal stresses where .the :extended surface .oins the tube.v distbutiunnftemperature gradientsin the extended surface so thatspiral-adcwrpassage spindles can be employed within finned and vshrouded .boiler elements safely. y

Figure 5 illustrates a portion pfthe tin J3 consistingfof a circular'disc I3 bearing a ilange '21 which merges intojan upwardly oiset rim 26 parallel to the disc I3. v An upturned circular flange I4 is formed at the center ofthe disc I3. A disc-shaped pocket 28 is thereby created. An orifice I5 is provided at the juncture cf the flange I4 .with the disc I3. 'I'he disc I3 is composed .of a heat and corrosion resistant material, such as nickeL and .is employed as a protective veneer furthe lower side ofthe n. Y

Figure 4 illustrates the flanges I4 pressed along Vdiieiube' 14 ina pile, therein( spacing. thens 13. nnnished :En x13a-is.illustrated as havl5` The-'invention however maintains even .Y

fluid course within the tube 'I4 effectively cools transverse fins thermally bonded thereto, eachl of said ns consisting of a disc of relatively high strength at elevated temperatures having a flange around its inner diameter, a second flat disc of relatively high strength at elevated temperatures spaced from said rst disc, and a third .disc cf relatively high thermal conductivity betweensaid .first and second discs', said ilrst and second discs cooperating to form Va. 'protective coveringicrsaid'third disc and said tube.

2..Boiler heat exchange apparatus comprising a thin walled tube having a plurality ofv spaced `apart transverse fins thermally bonded thereto.

1 said iirst and third discs cooperating to form a 'ingamlatively'thick Aring'l in Lthe '-J surrounds.

The fabrication process is undertaken Vin a 'controlled atmosphere furnace at approximately 2100 F. after which all the fins are changed in appearance from that of iin 13a to that of a completed n 13b'.V

The ring I 2 melts, thereby lling the pocket 28 and-allowing the disc III to sink against the rim 26 so that these parts are sweated together. Likewise liquid copper ows upward by capillary action to form a fillet I6 between the bore Il and the ange I4. Liquid copper also seeps through the orifice I5 sweating the flange I4 to the tube 14. Some of the copper from the orifice I5 forms a iillet I8 joining the bottom of the d isc I3 to the flange I4 of the next lower n. The described iin structure yields high thermal conductivity due to the use of the copper iilling, yet protection of the fin is provided by the veneer of corrosion and heat resistant metal. Copper has a thermal conductivity many times that of the best veneer materials. The copper` filling permits the use of very thin ns of large diamv eter accompanied by only a very small temperagated casing 54 closely encompassing theA cuterl diameter of the ns becomes red hot, tending to prevent re-radiation from the outer edges of the heat resistant veneer, whereas the helical boiler protective covering for said second disc and said ltube. f

"3.'In boiler heat exchange Aapparatus a thin walled having' .surface extending .means comprising a plurality of transverse ns'ther thereto, each of said fins consist- ...ing-afa disc of high durability at elevated temperatures having an up-turned flange around its inner diameter and an cli-set rim around its outer diameter, said flange and said rim cooperating to form an annular depression, a second iiat disc of high thermal conductivity substantube having a plurality of transverse ns thereon, each of said ns comprising a disc having an up-turned flange around its inner diameter and an ofi-set rim around its outer diameter, said.

flange and said rim cooperating to form an annular depression in said disc, a plurality of circumferentially spaced openings in said up-turned flange communicating with said annular recess, a second disc substantially iilling said recess, and a third disc cooperating with said first disc to Vform a protective .covering for-said second disc and said tube, the entire assembly being bonded.

into a substantially integral unit.

5. In combination in a boiler, apparatus comprising a thin-walled tube having a plurality of spaced apart transverse circular fins thermally bonded thereto, each of said fins consisting of a disc of high durability at elevated temratures and of relatively low thermal expansivity having a flange around its diameter, a second flat disc of relatively high strength. at elevated temperature and of relatively low thermal expansivity spaced'from said iirst disc and a third disc of relatively high thermal conductivity and of relatively high thermal expansivity between said drical shroud closely enveloping said ns over a substantial portion of the outer diameter of said ns, an inlet opening in said shroud for admitting hot gasesof combustion to the space between said fins, an exit opening opposite said inlet openingin said shroud for allowing said gases to be expelled from the space between said fins, and a helical ow passage lying against the inner surface of said tube for transmission of boiler Working fluid.

NATHAN C. PRICE. 

